Injection device with dose indicator mechanism

1. An injection device comprising:

a. a housing having a longitudinal axis;

b. a dose selector capable of setting a dose to be ejected from the injection device;

c. a dose indicator comprising a units wheel operatively connectable to the dose selector so that rotation of the dose selector about the longitudinal axis also rotates the units wheel, and a tens wheel selectively engageable with the units wheel so that rotation of the units wheel also rotates the tens wheel; and

d. a biasing means for biasing the dose indicator axially-rearwardly in the housing,

wherein an internal surface of the housing is provided with a tens housing feature comprising one or more formations selectively engageable with corresponding features on the tens wheel to prevent rotation thereof,

and wherein the internal surface of the housing is provided with a units housing feature capable of moving the units wheel axially-forward against said biasing means such that the units wheel engages and moves the tens wheel axially-forward and free of said tens housing feature so as to allow rotation thereof.

2. The injection device of claim 1 wherein the biasing means is a spring.

3. The injection device of claim 1 wherein the units housing feature comprises a cam surface.

4. The injection device of claim 3 wherein the units wheel comprises an axially-rearwardly-extending formation for engaging said cam surface on the housing.

5. The injection device of claim 1 wherein said units wheel is selectively engageable with said tens wheel by means of one or more teeth on the units wheel engageable with corresponding teeth on said tens wheel.

6. The injection device of claim 5 wherein said formations and/or teeth are regularly spaced.

7. The injection device of claim 5 wherein said formations and/or teeth on the tens wheel are located at a rear end of said tens wheel.

8. The injection device of claim 5 wherein said tens wheel teeth for engaging the units wheel are located radially inwardly of the tens wheel formations for engaging the tens housing feature.

9. The injection device of claim 1 wherein the dose indicator is arranged concentrically about said longitudinal axis.

10. The injection device of claim 1 further comprising a medicament container.

11. The injection device of claim 10 wherein the medicament container comprises a pre-filled syringe or cartridge.

12. The injection device of claim 10 further comprising a medicament contained in the medicament container.

13. The injection device of claim 12 wherein the medicament is selected from the group comprising: antipsychotic substances including risperidone, hormones, antitoxins, substances for the control of pain, immunosuppressives, substances for the control of thrombosis, substances for the control or elimination of infection, peptides, proteins, human insulin or a human insulin analogue or derivative, polysaccharide, DNA, RNA, enzymes, antibodies, oligonucleotide, antiallergics, antihistamines, anti-inflammatories, corticosteroids, disease modifying anti-rheumatic drugs, erythropoietin, or vaccines, for use in the treatment or prevention of rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, ulcerative colitis, hormone deficiency, toxicity, pain, thrombosis, infection, diabetes mellitus, diabetic retinopathy, acute coronary syndrome, angina, myocardial infarction, atherosclerosis, cancer, macular degeneration, allergy, hay fever, inflammation, anaemia, or myelodysplasia, or in the expression of protective immunity.